Royal fans will be treated to a special television programme marking the Queen's 90th birthday over the Easter weekend.
The two-hour landmark programme, Our Queen At Ninety, will be aired on Easter Sunday evening by ITV.
It features contributions from the Prince of Wales and the Duchess of Cornwall, the Duke and Duchess of Cambridge, Prince Harry and other members of the Royal Family.
Prime Minister David Cameron and leading lights in the entertainment and sporting worlds will also appear.
It will include Kate's first solo broadcast interview since marrying William in 2011.
The Duchess says the Queen was "really thrilled" to hear she had given birth to a baby girl, Princess Charlotte, in May last year, adding: "I think as soon as we came back here to Kensington she was one of our first visitors here."
"George is only two-and-a-half and he calls her Gan-Gan. She always leaves a little gift or something in their room when we go and stay and that just shows her love for her family."
Kate adds that she had been feeling "rather apprehensive" about a visit to Leicester without her husband, but her mother-in-law had been "very supportive".
"The fact she took the time to make sure that I was happy and looked after for that particular occasion, which probably in everything that she's doing is a very small element, it shows just how caring she is, really."
The Queen turns 90 on April 21. She will celebrate her official birthday in June with a mass street party in The Mall, a service of thanksgiving at St Paul's Cathedral and the traditional Trooping the Colour ceremony.
A four-day celebration in the grounds of Home Park, Windsor Castle, will take place on May 12 to 15.
William also shares fond memories of his grandmother, describing how people tend to become starstruck at meeting her.
He tells viewers: "A lot of people get very excited and sort of nervous around her. And I've seen some very comical moments. I've seen people literally faint in front of her. It's quite a startling moment as to what to do when you faint in front of the Queen.
"There's a lot of trembling knees and people can't talk sometimes. It's quite difficult talking to people when they can't talk. You don't get very far, I don't get past the hellos."
:: Our Queen At Ninety will be broadcast on ITV at 8pm on Sunday March 27.